Combustion method and apparatus



Patented Feb. 16, 1954 UNITED STATES PATENT OFFICE COMBUSTION METHOD AND APPARATUS Rallston M. Sherman, Glastonbury, Conn., assignor to The Silent Glow -il Burner Corporation, Hartford, Conn., a corporation of Connecticut Application September 10, 1949, Serial No. 115,090

11 Claims. (01. 158-4) secure complete combustion of the oil while securing a high temperature of the gaseous combustion products and an incandescent surface constituting a source of radiant heat of high intensity.

The invention, however, will be best understood from the following description when read in the light of the accompanying drawing of a specific embodiment of apparatus according to the invention for practising the method according to the invention.

According to the invention, the oil in an atomized state commingled with air, to form a mixture such as that produced by the ordinary domestic gun burner, is entered into a combustion chamber and burned therein, the chamber having walls comprising heat refractory sheet metal,

this'sheet metal, the opposite sides of which are exposed to the interior and exterior of the chamber, presenting an extensive area provided with closely spaced perfortaions distributed thereover for escape of products of combustion from the chamber. This perforated sheet metal, which preferably is formed of steel having a high chromium content, may, in respect to thickness and the diameter and spacing of the perforations, be, for'example butwithout limitation thereto, identical with that of which the combustion tubes of range oil burners commonly are formed. In this combustion chamber the oil, according to the invention, is burned with a flame of such pattern that it does not contact the combustion chamber walls, the on being burned at such rate that the perforated area of the sheet metal throughout its extent is heated to incandescence. say from 900 to 1500 F. The chamber is substantially closed so that substantially the only air which enters it is that which is contained in the atomized oil-air mixture, and preferably is so constructed that the only escape of the products of combustion is substantially through the small perforations mentioned.

It has been found that in burning the oil in the way above described complete combustion may be secured, the combustion products after the apparatus assume stable operation being constituted wholly by carbon dioxide, nitrogen, excess oxygen, and water vapor. The apparatus according to the invention, it has been found,

assumes stable operation in from about 200 to 250 seconds after combustion is initiated. During this short period small amounts of carbon monoxide are produced, but-not in dangerous amounts, to wit, only from about 5 to 10 parts per million parts combustion products. A typical analysis of the dry combustion product of apparatus according to the invention burning No. 2 fuel oil according to the improved method is as follows:

Percent Carbon dioxide 4.41 Illuminants None Oxygen 12.09 Hydrogen None Carbon monoxide None Ethane None Methane None Nitrogen 83.50

As a result of the absence of carbon monoxide monoxide in the combustion products, when burning oil according to the invention, the improved apparatus may be placed in a closed room or other space for heating it without danger to occupants of such room or space. This adapts the apparatus for use, for example, as a space heater in barns, potato storage houses, and the like, the same being heated by the products of combustion issuing through the above mentioned perforations of the combustion chamber and by the radiant heat emitted from the incandescent surface portions of the walls of that chamber. Furthermore, because of the total combustion of the oil, the products of combustion are entirely odorless, making it possible to heat such a space without contamination of the crop or other material stored in such space.

It has been found that the diameter of any perforations, including those above mentioned, in the combustion chamber wall permitting escape of combustion products should not exceed approximately 0.15 inch in diameter, or otherwise have a cross-sectional area greater than approximately that presented by a perforation of such diameter, namely, a cross-sectional area of approximately 0.018 square inch, as otherwise incompletely burned combustion products will escape through them usually in the form of a smoke having apronounced odor and containing dangerous amounts of carbon monoxide. The perforations may have, diameters as small as possible, and preferably are as small as can be economically produced. For practical and economic reasons these perforations are formed by use of a punching operation employing a multiple die which forms a large number of perforations at each punching stroke, and under any ordinary condition it is not practical to so punch them with diameters much less than about 0.08 inch. Otherwise, and with smaller perforations, the perforations would have to be formed by expensive and time consuming drilling operations. Excellent results are obtained with twenty uniformly distributed perforations per square inch each of 0.078 inch diameter. It has. been found, however, that the number of perforations and their sizes, whether produced by punching .or drilling, may be varied solong as the total area presented by the perforations per square inch is from approximately 0.05 to 0.14 square inch.

Preferably the sheet metal'constituting the perforated portion of the combustion chamber is as thin as structural requirements will'permit, sheet metal about s? inch thick giving satisfactory results in most situations. However, this thickness is not critical, and may be varied within wide-limits.

It also has been found that to secure complete combustion the cubical contents of the combustion chamber or drum should be from approximately 2300 to 4000 cubic inches per gallon of oil burned per hour, with the total perforated surface of the drum, 1. e., the area of the perforations and the intervening metal, expressed in square inches from 15 to 35%. of the arithmetical value .ofqthe cubical contents of the combustion chamber or drum expressed in cubic inches.

The kind of oil burned in the improved ap paratus in practising the. improved method is not critical, satisfactory results havingbeen secured with ordinary commercialgasoline, kerosene, and all grades offuel oil up to so-called No. 3 fuel .o'il.

Preferably the combustion chamber for structural reasons is in the form of a cylindrical drum having closed ends, through one of which ends the atomized oil-air mixture is entered, this end preferably being otherwise imperforate. Also the perforated portion of the combustion chamber or drum is preferably constituted by the cylindrical or other lateral walls of the drum. The end of the drum opposite that end through which the oil-air mixture enters may, if desired, be perforated so as to constitute part of the perforated portion .of the drum. However, perforating this end of the drum seems'to secure no use ful effect in any ordinary case except. in reducing the starting period for the apparatus to assume stable operation.

When a cylindrical drumis employed therelation between the diameter of the drum and its length is by no means critical, satisfactory re sults having been secured where thelength of the drum is from 100 to e%"of,its diameter. Examples of having their lengths within such range are drums .15 inches in diameter and 18 inches long, 22 inches in diameter and 24 inches long,,22 inches in diameter and 36 incheslong, and 26 inches in diameter. and 30 inches long. Gther proportions between the length and diameter of the drum however may be employed, and satisfactory results have been secured .with drums thelength of which is less thantheir di ameter, for example, with drums 22 inches in diameter and 18 inches long, in which particular instance the length of the drum isbut about 80% of its diameter.

The amount of air admixed with the atomized oil may be that commonly employed in; connect with mesti oil burners. nteierably al of air supplied at; a minimum consistentwith securing satisfactory operation, as'otherwise the temperature of the combustion products will be decreased. In accordance with common practice this amount. of ,air, should be such as to give a rather small amount of excess oxygen in respect :to the amount thereof which will stoichiometrically. secure complete combustion, namely, from 8-to 15% excess oxygen, but preferably from about to'l2%.

"In practising. the improved method with combustion chambers designed as above described thepressure within the chamber is only very slightly above that ofithe surrounding atmosphere, 1 under ordinary circumstances ithis' pressure being only from about9-0.0008 to 0.006 inch of water abovethat of the surrounding atmos phere.

Examples-of apparatus according to the invention for practising the improved method-are shown by the accompanying drawings: in which Fig.1v is an, elevation, with parts brokenaway,

of such apparatus; and

Fig. 2 is an end View showing a modified form of the combustion chamber,1corresponding .to Fig.

.1 as viewed from the *rightwith parts omitted.

Referring to Fig. I of: the ;drawings,1ztheicombustion chamberis-in-the form of a drum. having the cylindricalwall l-provided-withperiorations 3 distributed over its entire surface. As shown,

the end: 5, of the: drum is closed; whilectheaend 1 is provided with any opening v9 which receives the discharge end of va conduit ll :throughthe open end'l3 of which the. atomized oileair mixture is. discharged into: the drum. As illustrated, the conduit ll forms-part of za conventional gun type burner, this burner comprising. acasing containing an electriczmotordriven fan for forcing .air. through the conduit I I-into'thedrum,

the amount of air being regulated in the usual mannerby adjustable shutters (not shown) :on

the end .of the casing, which shutters controlxthe size of the air intake to'the fan. As in thereonventional gun typeburner, a pump l9, .drive.n..bl the same motor as the fan drawso-ilfrom the tank 2| and discharges it underpressure' into a pipe'*23 in communication with a pipe positioned axially of the conduit-l l,thepipe 25 having at its end adjacent the combustion chamber or drum a spray nozzle 2'! for .atomizingthe ;oil. This nozzle is sodesignedas to=secure the desired pattern of the flame and the desired amount of oil supplied the combustion chamber. FPreferably positioned inathe conduit H is'a circumferential series of vanes 29'for causing a whirling'ac'tion of the air dischargedfrom the conduitsoasthoroughlyto mix the air withthe'atomized .oil. The burner, as shown, is provided with :an ignition .spark electrode 3 l, and preferably is providedwith the usual controls for governing the-operation of the apparatus in accordance with the temperature conditions of the space heated.

If desired, theopening -Qin theend .Tof the drum may-be slightly larger :than the exterior diameter of the conduit 1 I so as to permitexpansioniof; the par s- .S me air mavflow-into the .drum through he clearance afforded .by this openinsbecause of the, suction effect ofthe-mixturc --en cring 1th. drum-from theconduit 1v ll.

and such air will mix in substance all the air which enters the drum is contained in the oil-air mixture supplied it.

with the mixture so that Although only the cylindrical portion of the drum is perforated in the form of apparatus shown by Fig. 1, the end 5 thereof also may be perforated, as above explained and as shown at '3 in Fig. 2. As an example of the invention in formly spaced to present twenty perforations per square inch, the apparatus under conditions of satisfactory minimum oil consumption burning 1.65 measured gallons of No. 2 fuel oil per hour, the amount of air supplied being sufficient to produce a bright orange flame, this amount of oil heating the walls of the combustion chamber to between 1300 and 1400 F.

It will be understood that within the scope of the appended claims wide deviations may be made from the forms of the invention described without departing from the spirit thereof.

What is claimed is:

1. The method of burning fuel oil to secure substantially its complete combustion without formation of carbon monoxide, utilizing a combustion chamber consisting of a drum of thin heat refractory metal exteriorly defined by lateral and end walls, which lateral walls are formed with perforations not exceeding approximately 0.018 square inch in transverse cross-section and distributed over said lateral walls in spaced relation in such number as to present approximately from 0.05 to 0.14 square inch of total transverse cross-section per square inch of perforated surface, with the total area of such surface in square inches being arithmetically approximately from 15 to 35 per cent of the arithmetical value of the cubic contents of the drum expressed in cubic inches, which method comprises burning the fuel oil in said drum by, discharging it into the drum atone end thereof toward its opposite end in atomized state mixed with sufficient air to support its complete combustion, at the rate of one gallon of such oil per hour for each 2300 to 4000 cubic inches of the cubic contents of the drum, and in the form of a spray of such pattern as will produce a flame that is in such proximity to at least the lateral walls of the drum as to heat them to incandescence but is in out-of-contacting relation with all said walls of the drum so as to be surrounded by combustion products, such air being substantially the only air admitted to said drum; and discharging the combustion products from said drum substantially solely through said perforations.

2. The method according to claim 1 in which the drum utilized also has lik perforations in its end wall opposite its end wall through which the mixture of atomized fuel oil and air is entered, which perforations also present approximately from 0.05 to 0.14 squar inch of total transverse cross-section per square inch of perforated surface, the total area of perforated surface presented by said perforated end Wall and lateral walls in square inches being arithmetically approximately from 15 to 35 per cent of the arithmetical value of the cubic contents of the drum expressed in cubic inches, the spray being of such pattern that th flame produced also is in such proximity section per square inch to said'perIQrated end wall as to heat it also to incandescence and the combustion products being discharged substantially solely through the perforation of said lateral walls and perforated end wall.

3. Oil burning apparatus comprising a combustion chamber in the form of a drum of thin heat refractory sheet metal capable of being heated to incandescence, such drum being exteriorly defined by lateral and end Walls, the lateral walls being formed with perforations constituting substantially the sole means of escape of combustion products from said drum, said perforations not exceeding approximately 0.018

square inch in transverse cross-section and distributed over said lateral walls in spaced relation in such number as to present approximately from 0.05 to 0.14 square'inch of total transvers crossof perforated surface, with the total area of such surface in square inches being arithmetically approximately from 15 to 35 per cent of the arithmetical value of the cubic contents of the drum expressed in cubic inches, one end wall of the drum having an opening; burner means for discharging into said drum through said opening atomized fuel oil mixed with suflicient air to support it combustion at the rate of one gallon of such oil per hour for each 2300 to 4000 cubic inches of the cubic contents of said drum; said burner means comprising an oil atomizing spray nozzle associated with said opening, from which nozzle the oil is so discharged, and also comprising an air supply conduit associated with said opening and nozzle for supplying the air of such mixture, a pump for supplying said nozzle with the fuel oil and a blower for supplying said conduit with air, the nozzl being constructed to form an oil spray of such pattern that the flame produced by the burning of said mixture within the drum will be in out-of-contacting relation with all said Walls of said drum, said air supply conduit constituting substantially the sole means of admitting air to said drum.

4. Oil burning apparatus according to claim 3 in which that end wall of the drum which is opposite the end thereof having the opening with which the spray nozzle is associated is also formed with spaced perforations, which perforations also do not exceed approximately 0.018 square inch in transverse crosssection and present approximately from 0.05 to 0. 4 square inch of total transverse cross-section per square inch of perforated surface, the total area of perforated surface presented by said perforated end wall and the lateral walls in square inches being arithmetically approximately from 15 to 35 per cent of the arithmetical value of the cubic contents of the drum expressed in cubic inches, the perforations of the lateral walls and of said perforated end wall constituting substantially the sole means of escape of combustion products from the drum.

5. Oil burning apparatus according to claim 3 in which the lateral walls of the drum are substantially cylindrical.

6. Oil burning apparatus according to claim 3 in which the lateral walls of the drum are substantially cylindrical and the end wall of the drum opposite the end wall with which the spray nozzle is associated lies substantially in a plane normal to the longitudinal axis of the drum.

7. Oil burning apparatus according to claim 3 in which th lateral walls of the drum are substantially cylindrical and each end wall lies subwhich the spray nozzle is associated is-also transverse crossesection and ,metically approximately which is opposite .to the longitudinal axis .Lof perforated surface,

istantially. in a plane normal to I the longitudinal axisof the drum.

'8. Oil burning apparatus according; to claim :3 in-which that end Wall of the drum which is opposite the end thereof having the opening with formed withspacedperforations, which perforations also do not exceed approximately 0.018 square inch in present approximately from 0.05 to 0.14 square inch of total transverse cross-section per-square inch of perforated surface, the total area of perforated, surface presented by said perforated end wall and the lateral walls in square inches being arithfrom 15 to 35 per cent of the arithmetical value of the cubic contents of the drum expressed in cubic inches, the perforations of the lateral walls and of said perforated end'wall constituting substantially the sole means of escape of combustion products from the drum. 9. Oil burning apparatus according to claim 3 in which the lateral walls of the 'drum arecylindrical and in which that end-wall of the drum the end thereof having the opening with which the spray nozzle is associated is also formed with spaced perforations, which perforations also do not exceed approximately 0.018 square inch in transverse cross-section and present approximately from 0.05 to 0.14 square inch of total transverse cross-section per square inch of perforated surface, the total area of perforated surfac presented by said perforatedend wall and the lateral walls in square inches being arithmetically approximately from 15 to 35 per cent of the arithmetical value of the cubic contents of the drum expressed in cubic inches, the perforations of the lateral walls and of said perforated end wall constituting substantially the sole means of escape of combustion products from the drum.

10. Oil burning apparatus according to claim 3 in-which the lateral walls of the drum are substantially cylindrical and in which that end wall of the drum which is opposite the end thereof having the opening with which the spray nozzle is associated lies substantially in a plane normal of the drum and is also formed with spaced perforations, which perforations also do not exceed approximately 0.018 square inch in transverse cross-section andpre- ,sentapproximately from 0.05 to 0.14 square inch of total transverse cross-section per square inch the total area of perforated surface presented by :saidperforated :end 'wall 1 and the lateral walls in square inches being arithforations of the lateral walls and of saidperforated end "wall 1 constituting substantially the sole ymeans of escape .of combustion products fromthe drum.

llhoilburningapparatus according to claim 3v in-which the lateral walls of the drum are substantially cylindrical and in which each end wall lies substantially in a plane normalto the longitudinal axis of the drum and is also formed with spaced perforations, whichaperforations also .do not exceed approximately 0.018 squareinch. in transverse cross-section and present approximately from 0.05to 0.14square inch of total transverse cross-section per square inch .of perforated surface, the total area of. perforated surfacepresented by said perforated endvwallrand the lateral walls in square inches being arithmetically approximately from 15 to 35 percent of the arithmetical value of the cubic contents ofthedrum expressed in C b in her rforationsof .the lateral walls and of said .perforated end wall constituting.substantiallythe sole means of escape of combustion products from the. drum.

RALLSTON M. SHERMAN.

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